Recently, there have been proposed and developed various magnetic tape cassettes to serve as a data storage medium.
One such magnetic tape cassette is disclosed in U.S. Pat. No. 4,198,013. This conventional tape cassette includes a supply reel and a take-up reel rotatably supported in a cassette casing. Typically, upstanding tape guide pins are utilized in such tape cassettes to define a tape path for the magnetic tape. The guide pins are affixed in predetermined locations in the cassette casing such that the tape is wound onto the reels at a predetermined contact angle.
Conventional guide pins for tape cassettes are disclosed in U.S. Pat. No. 5,097,374 entitled TAPE CASSETTE HAVING TAPERED GUIDE PINS PRESS-FITTED INTO CASSETTE WALL AND GREASE LUBRICANT FOR ROLLERS which issued on Mar. 17, 1992 to Koizumi et al. and is assigned to Sony Corporation. Referring to FIG. 1, a first configuration for a conventional guide pin 90 is shown. The tape cassette includes a lower cassette casing 92 shown as a partial cross section having a hole 104 which includes an inner periphery 110. The guide pin 90 includes a tape contact section 94 positioned between an upper flange section 96 and a lower flange section 98 having a bottom surface 102. The tape contact section 94 provides a contact surface upon which magnetic tape (not shown) passes over as the tape is advanced within the tape cassette. The upper 96 and lower flange 98 sections serve to restrict lateral movement of the tape as the tape passes over the tape contact section 94. A press-fit section 100 extends downwardly from the bottom surface 102. The tape contact 94, upper flange 96, lower flange 98 and press-fit 100 sections each have a constant outer diameter. The outer diameter of the press-fit section 100 is sized larger than the hole 104 so as to provide a press fit upon insertion of the press-fit section 100 into the hole 104. This causes pressure between the press-fit section 100 and inner periphery 110 which serves to affix the guide pin 90 to the cassette casing 92.
Referring to FIG. 2 in conjunction with FIG. 1, a partial view of a second configuration for a conventional guide pin 112 is shown. In this configuration, the guide pin 112 includes a press-fit section 114 having an outer diameter which gradually increases from the bottom surface 102 to an end 106 of the press-fit section 114 to form a reverse tapered outer periphery 108. As such, an outer diameter (a) near the bottom surface 102 is smaller than an outer diameter (b) at the end 106 of the press-fit section 114. Upon insertion of the press-fit section 114 within the hole 104, the hole 104 expands to accomodate the outer diameter (b) of the press-fit section 114. As a result, areas of the press fit section 114 having an outer diameter smaller than outer diameter (b) do not come in contact with the hole 104. Consequently, the entire outer periphery 108 of the press-fit section 114 is not in contact with the entire inner periphery 110 of the hole 104, thus decreasing the amount of pressure therebetween. This results in a relatively loose press-fit wherein the guide pin 112 may be easily removed. As such, vibration and other external forces may undesirably dislodge the guide pin 112 from the cassette casing 92.
Referring to FIG. 3, a third configuration for a conventional guide pin 116 is shown. In this configuration, the guide pin 116 includes a press-fit section 118 having an outer diameter which gradually decreases from the bottom surface 102 to the end 106 of the press-fit section 118 to form a frusto-conical or tapered outer periphery 118. As such, an outer diameter (A) near the bottom surface 102 is larger than an outer diameter (B) located a distance 1 from the outer diameter (B) near the end 106 of the press-fit section 118. It is desirable that the taper of the press-fit section 118, denoted by (A-B)/(l), be selected within a range of ratios between 1/250 and 1/38. If the taper exceeds the maximum value, the flatness of the cassette casing 92 may not be maintained due to high stresses produced upon insertion of the press fit section 118 into the cassette casing 92. Alternately, if the taper is less than the minimum value, a sufficient press fit may not be achieved.
Furthermore, it is desirable that the dimensions of the press-fit sections are maintained within close tolerances to ensure a sufficient press fit. This requires high precision manufacturing techniques. Typically, a lathe is used to manufacture the conventional guide pins. However, the machining accuracy of a lathe is undesirably affected by various factors. These include deflection of the guide pin that occurs during machining, fluctuation in bite of the cutting tool utilized, inconsistent application of cutting lubricant on the guide pin and others. A further disadvantage is that maintaining a high degree of machining accuracy results in high manufacturing costs and is time consuming.